Directive high-frequency antenna



Patented Aug. 30, 1949 DIRECTIVE HIGH-FREQUENCY ANTENNA Stanley L. Breen, Cambridge, Lan Jen Chu, Brookline, and, Chia-Shan Pao, Cambridge, Mass., asslgnors, by mesne assignments, to the United States of America as represented by the Secretary of War Application January 24, 1945, Serial No. 574,368

2 Claims. 1

The present invention relates to an antenna for use in a high frequency communication system and is particularly directed to an antenna adapted to discontinuously scan portions of space. Y

Accordingly,the principal object of this invention is to provide an antenna which is` adapted to radiate electromagnetic waves of high frequency energy in a distribution pattern which shifts in discrete steps through a plurality of regions in space rather than scanning continuously.

It is also an object -of the invention to obtain a discontinuous scan by providing a group of spaced radiating elements and means for radiating energy from one or more of the elements in a predetermined arrangement or sequencel to provide a variety of scanning patterns.

It is another object ofthe invention to provide an antenna adapted to discontinuously search a portion of space and which is economical to construct and easy to operate.

Dther objects and advantages of this invention will become apparent as the description proceeds, reference being made to the accompanying drawings in which:

Fig. 1 is a side elevation view, partly broken away, of one embodiment of an antenna according to the invention; with a circular wave guide,

and with a parabolic reflector shown diagram- Fig. 3 is a sectional view, partly broken away,

of said reflector taken on the line 3-3 of Fig. 2.

Referring to the drawings, a parabolic reflector is diagrammatically indicated at I ll in Fig. 1. Mounted in front of reflector I is a circular hollow wave guide II, adapted to be excited by energy from a source (not shown), preferably in the TEM mode and polarized as indicated in Fig. 3. the arrows E representing the direction of the electric lines of force. Wave guide II is generally disposed so thata plane tangential to its surface and perpendicular to the axis of reilector I0 passes through the focal point F of reflector Ill.

A plurality of slots are disposed inthe wave guide II and are symmetrically spaced about and near the focal point F. As shown more clearly in the exciting energy so that the slots are properly matched to space. Energy from guide Il is adapted to be radiated from the respective slotstoward the reflector Ill from which it is reected into space in a directional manner.

Mounted coaxially relative to guide II is a cylindrical sleeve or collar member I6. Sleeve I6 surrounds the guide Il in closely tting relation thereto over a substantialportion of the length of the guide II. Sleeve member I6 is rotatably mounted relative to guide Il in any suitable manner such as by a ball bearing raceway generally indicated at I1 in the broken away portion of Fig. 1. Any suitable means may be used for rotating sleeve IB about guide I I for example, a ring gear I8 may be mounted on the lower peripheral surface of sleeve I6 mating with gear Fig. 2. guide II is provided preferably with four slots, l2, I3, I4 and I5, having their longitudinal axes parallel with the longitudinal axis of guide il. The length of each of the slots is generally a I9 and driven through shaft 20 by motor 2l.

vSleeve I6 is provided with a group of apertures or slots so disposed that only one of the apertures at a time will match or register with one of the slots in guide I I and the remaining slots in guide I I will be covered by the solid wall of cylindrical sleeve I6. For example, when guide II is provided with four slots, l2, I3, I4 and I5, as referred to above, sleeve I6 is preferably provided with four apertures 22, 23, 24 and 25. These apertures may be of any suitable dimensions, but preferably of substantially the same vertical dimensions as the length of the slots in guide Il.

As shown more clearly in Figs. 2 and 3, apertures 22, 23, 24 and 25 are spaced symmetrically in sleeve I6 with the width of the apertures, 1n the illustrated example, being equal to about a 40 arc of the peripheral surface of cylindrical sleeve I6. Apertures 12,2 and 24 are preferalznlyl disposed diametrically opposite to apertures 23 and 25 respectively, with adjacent apertures being disposed radially substantially 90 apart.

As shown, slots I2 and I3 and apertures 22 and 23 are located on one side of the axis of reiiector IIJ, and slots I4 and I 5 and apertures 24 and 25 are located on the opposite side of the reflector axis. Aperture 23 is shown corresponding with, or in registry with, slot I3; thus permitting radiation of energy from slot I3 toward reilector I0,

the remaining slots being closed and effectively short-circuited by the solid wall of sleeve I6.

As sleeve I6 is rotated, for example in a clockwise direction (Fig. 3), aperture 23 moves out of registry with slot I3 and into registry with slot I2, slot I3 thereby being closed by the wall of sleeve I6. Continued rotation brings aperture 25 into registry with slot I5 and then slot I4, and

half wavelength of the operating wavelength of aperture 22 into registry with slots I3 and I2 a path of radiation which makes an angle with the axis of the reiiector. The size of the angle, of course, is proportional to the amount the radiating slot is displaced from the focal point F. 1n the illustrated antenna having four radiating slots as shown, there are thus four separate paths of radiation adapted to be independently illuminated according to a predetermined sequence. Preferably the radiation pattern of each individiual beam overlaps the radiation pattern of one or more of the other beams. Such a system provides a scanning action of the portion of space included within the composite pattern of radia-A tion.

. By suitable arrangement of the mentioned apertures and slots any desired sequence of radiation from the slots may be provided. Thus any desired scanning pattern may be obtained by the present invention merely by suitably arranging the slots in the wave guide Il and the apertures in the sleeve I6.

Thus it will be apparent that as radiation occurs rst from one slot and then from another according to a predetermined arrangement, energy is radiated in a distribution pattern which shifts from section to section in space in a discontinu- While an embodimentof the invention is illustrateclV herein, it will be .understood that many different arrangements of any number of radiating elements, i. e. slots, wave guides, horns, etc., are possible with. the present invention. The elements may be fed in series or parallel, as desired. Similarly'any predetermined sequences of illumination of the elements may be used.

We claim:

1. An antenna for use in a high frequency communication system comprising, in combination, a parabolic reflector, a hollow circular wave guide adapted to transmit high frequency electromagnetic energy mounted in front of said reflector so that a plane tangential to its surface and perpendicular to the axis of said reflector passes substantlally through the focal point thereof, a cy lindrical sleeve rotatably mounted in closely tting coaxial relation around said wave guide, said wave guide having a plurality of slots spaced symmetrically with reference to said focal point, the longitudinal axes 0f said slots being parallel with the longitudinal axis of said wave guide,

the length of each said slot being substantially half the operating wavelength of the electromagnetic oscillations, said sleeve having a plurality of spaced apertures, and means for rotating said sleeve whereby said apertures are adapted to register successively with said slots in a predetermined sequence for permitting energy to be radiated from said slots one at a time, the remaining slots being closed and effectively shortcircuited by said sleeve, for thereby enabling said antenna to discontinuously scan in a distribution pattern which shifts in discrete steps through a plurality of regions in space.

2. An antenna as claimed in claim ,1 in which the wave guide is provided with four slots, said slots being spaced symmetrically with reference to the focal point of the reflector, two of said slots being parallel to each other on one side of the axis of said reflector, the other two of said slots being parallel to each other on the opposite side of the axis of said reflector, and in which the sleeve is provided with four apertures, the length of each aperture being substantially equal to the length of said slots and the width of each aperture-being substantially wider than the width of said slots, two of said apertures being located diametrically opposite each other and adapted to be rotated into registration with said rst-mentioned two slots, the other two of said apertures being located diametrically opposite each other and adapted to be rotated into registration with said second two slots. 'f

STANLEY L BREEN.- LAN JEN CHU. CHIA-SHAN PAO.

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